<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 100px;
            height: 100px;
            border: 5px solid red;

            display: block;
        }
        span{
            background-color: #ff0;
            width: 200px;
            height: 200px;
            /*行内元素不能设置宽高 横着排*/
            display: inline;
            /*可以切换元素的显示模式*/
            display: block;
        }
        input,button{
            /*行内块元素 既能横着排 又可以设置宽高*/
            display: inline-block;
            width: 200px;
            height: 200px;
        }
        .d2:hover{
            display: none;
        }
    </style>
</head>
<body>
<div class="d1">111</div>
<div class="d2">222</div>
<div class="d3">333</div>
<hr>
<span>123456789</span>
<span>123456789</span>
<span>123456789</span>
<hr>
<input type="text">
<input type="text">
<input type="text">
<button>按钮</button>
</body>
</html>